1. Field of the Invention
The present invention relates to the measurement of gasoline volatility characteristics, and more particularly to an ultrasonic-type gasoline characteristic determination method and apparatus capable of determining the volatility characteristics with good accuracy by measuring the velocity of an ultrasonic wave in a gasoline containing alcohol or other additives and by compensating for deviations from a reference temperature.
2. Description of the Prior Art
Among the characteristics of automotive gasolines, the ability to resist knocking in engines is one of the important quality-determining characteristics. To increase this anti-knocking ability, tetra ethyl lead (TEL) is added, but in recent years, gasolines containing about 10% ethyl alcohol instead of TEL have been used in the United States and other countries.
Gasoline, in itself, is not always uniform, but there are variations in its volatility (combustion properties). The T50 value used to describe this volatility indicates the temperature at which 50 percent of the gasoline evaporates, the T50 value being lower for lighter gasolines. In accordance with this T50 value, i.e., volatility, engine control must be optimized. For example, if the volatility before engine startup can be determined, it becomes possible to minimize the amount of fuel increase during engine startup and thus reduce emissions during the startup.
In particular, gasolines used in the United States have varying degrees of volatility, and it is essential to optimize engine control according to the volatility. The need therefore arises for a sensor capable of monitoring gasoline volatility. The T50 value that serves as a measure of gasoline volatility is estimated from gasoline density. This density is calculated from the propagation time of an ultrasonic wave.
In Japanese Unexamined Patent Publication (Kokai) No. 7-225228 as one prior art pertaining to this field, a detection device is installed midway through a gasoline pipeline, and noting the fact that gasoline volatility tends to become higher for softer gasolines with lower densities, the propagation delay time of an ultrasonic wave is detected to obtain the gasoline density, thus measuring its volatility properties and estimating the T50 value.
This method, however, has not been sufficient in terms of accuracy since for gasolines containing additives such as alcohol, the relationship between the density and the T50 value is not constant but an inversion occurs. There is therefore a need for a simple gasoline property determination method and apparatus with improved accuracy.